“Mileage run” definition:
A mileage run is a strategy used by members of airline frequent flyer programs to rapidly accumulate award miles or points by flying as many miles as possible in a short amount of time. Successful mileage runners are often experts in airline routing and can find or construct flight routes that allow maximum mileage accumulation. A low price is also an important consideration when mileage running; typically desirable fares are those that cost less than 4 cents per mile.
Mileage runners try to accumulate two types of miles or points: miles that can be used to purchase future flights and miles that count toward elite status qualification. In the US, Delta Air Lines and United Airlines have recently made mileage runs more difficult to find and less attractive overall with the introduction of revenue-based “miles” earning (as opposed to the old model – earning credit toward future flights based on actual miles flown) as well as minimum annual spending requirements.